Silver Nanoparticle Sorption and Desorption to Soil and Water Treatment Residuals.

Nanoparticles are known to be toxic to organisms in a laboratory environment, but studies have shown that toxicity levels shown in laboratory conditions are not the same as in a natural environment. The fate of nanoparticles in the environment is not clear, and more research needs to be done to determine if and how they accumulate in soils, sediments, plants, and other organisms.  This goal of this research was to investigate the sorption and desorption of silver nanoparticles onto soil and water treatment residuals.  Sorption studies were conducted using 10nm and 90nm monodispersed silver nanoparticles in 2mM sodium citrate buffer as well as <90nm silver nanoparticle powder.  The sorption media used were two soils (Plano silt loam and a locally available “black wetland topsoil”) and a water treatment residual (WTR – product of drinking water treatment process). The soil particle size that the nanoparticles were associated with was also investigated. Preliminary results indicated that the wetland soil and WTR were able to adsorb more silver nanoparticles than the silt loam soil and seemed to be related to carbon content. In the WTR AgNPs were associated with sand size particles (2mm – 0.05mm), but in the wetland soil and silt loam, approximately half of the AgNPs were associated with the sand-sized particles, while the rest were associated with silt sized (~0.05mm) or smaller particles.  The larger sorption capacity of the wetland soil and WTR was attributed to their higher carbon content. Desorption studies indicated that the media were dissimilar in their ability to retain silver nanoparticles. The sorption data indicate that AgNPs adsorbed to soil and WTRs and support the idea that natural and constructed wetlands can remove AgNPs from wastewater.